Embodiments described herein relate generally to radiation-redirecting external cases for mobile communication devices such as cell phones, smartphones and similar handheld devices.
Design requirements of mobile communication devices place an increasing premium on the available antenna space within these devices as their functions become more diverse, ranging from the original basic function as a wireless telephone to a music player, video player, handheld computer, wireless internet device for browsing the web, retrieving email and downloading or uploading files, a still camera, a video camera, a GPS device, a navigation system, etc. Some of these functions involve transmission and reception of wireless signals including voice information, data signals, and/or navigation information. Voice and data signals can include, for example, 2G, 3G, and/or 4G signals. The signals can also include WiFi® signals, Bluetooth® signals, or global positioning satellite (GPS) data. As more spectrum is made available to cope with the demands of data transmission, antennas are frequently multi-band or broadband in frequency—all of which can compromise antenna efficiency.
In addition, radio frequency (RF) radiation from mobile phones is becoming of greater concern as a health risk. Partially for safety reasons, the FCC requires limiting the radiation from a mobile communication device (such as a mobile or cellular telephone) that is directed towards a user's head (Specific Absorption Rate, or SAR). As wireless communication technology advances, however, the mobile communication device has increasing data-intensive functions, involving high rates of data transfer between the cell phone and the base station tower. Because increasing the power output of the antenna is typically difficult without increasing the SAR, and because limited space exists on board the wireless communication devices to include components reducing RF radiation in the direction of the user while improving RF signal, a need exists for an external device that includes an improved antenna system for redirecting RF radiation from a user's body and/or strengthening antenna signal in both the transmission and reception of signals. An external antenna system can also be used to improve the device antenna efficiency at frequencies of interest.
For a more “premium” aesthetic, mobile devices can be made with a metal chassis—an architecture in which the chassis itself functions as (or be part of) the antenna structure. As a result, changing the environment of the chassis (e.g., held in the human hand, or enveloped in a plastic case) can adversely affect antenna efficiency. This outcome can be mitigated to some degree with internal active tuning components—but such hardware adds to the complexity, space requirements and cost of the device.